Coherent optical receivers process traffic, in the form of optical signals, received from an optical network. Coherent optical receivers process the optical signals by performing operations on the optical signals, such as polarization beam splitting, demodulation, analogue-to-digital conversion, etc. The processing usually includes coherent processing using a local oscillator that is matched to a carrier frequency that is generated by a remote oscillator in an optical transmitter.
Coherent optical receivers use a carrier recovery technique, such as feedforward carrier recovery (FFCR), for tracking phase difference between the remote and local oscillators. The difference in phase (e.g., phase noise) may be associated with phase noise from the remote oscillator, the local oscillator, and/or the optical path (e.g., optical fiber) that interconnects the optical transmitter to the receiver. However, the performance, associated with the FFCR technique, is sensitive to how well a filter, used by the coherent optical receiver to smooth the recovered phase, is matched to the noise characteristics of the signal.
FFCR may, however, introduce cycle slips that are caused by a transient loss of phase lock, by a carrier recovery loop circuit, within the coherent optical receiver. The cycle slips can cause bit errors to occur when processing the signal. While the errors may be correctable, the cycle slips may increase a quantity of risk, associated with an occurrence of an uncorrectable frame and/or loss of data, as a result of a cycle slip.